1. Field of the Invention
The present invention relates to a method for constructing a very deep shaft having a depth of more than hundreds of meters. Further, the present invention is concerned with a machine suitable to perform the method above.
2. Prior Art
In order to construct such a deep shaft, work must be performed in steps: a step of approximately vertically excavating a soft rock to form a shaft and then a step of excavating muck generated by excavation of the shaft. With such a method, it is critical how to convey efficiently the muck out of the shaft because the efficient conveyance of the muck serves to reduce the term and cost of the construction of the shaft.
Known processes for conveying the muck are as follows:
(1) introducing the muck into a kibble or a bucket at the bottom of the shaft and then lifting it upward to the inlet of the shaft.
(2) filling the shaft with water and then raising the muck and the water upwards by means of an air-lifting pump.
(3) filling the shaft with water and pumping up the water including the muck by a method, called the reverse circulation method, and then separating the muck from the water.
Such conventional processes however have drawbacks. With the process (1), the conveyance of the muck can be merely intermittently performed and it takes much time to raise and lower the kibble or the bucket Therefore, the process (1) cannot be used as a process for constructing efficiently a shaft of a great depth.
With the processes (2) and (3), the conveyance of the muck can be continuously performed because the muck can be lifted up to the inlet of the shaft by filling the shaft with water. However, a peripheral wall of the shaft cannot be subjected to a primary lining or shotcrete made of a concrete because the shaft is filled with water. Also, an expensive excavator having properties such as watertightness, waterproofness and the like must be used for construction of the shaft. Further, the excavator must be drawn up when maintenance is done on the excavator outside of the shaft, or the water filled in the shaft must be pumped out when the maintenance is done in the shaft.
With such conventional methods, the muck in the bottom of the shaft cannot be efficiently conveyed outside thereof.